1. Field of the Invention
The present invention relates to a marine drive, and more particularly to an improved shifting mechanism for a transmission of the marine drive.
2. Description of Related Art
Outboard motors typically include a power head supported by an upper housing. A clamping bracket usually secures the upper housing to a transom of an associated watercraft. The upper housing also supports a lower unit that includes a propeller or similar propulsion device. An engine within a cowling of the power head drives the propeller via a drive train. The drive train commonly includes a drive shaft, which extends generally vertically through the upper housing, and a propeller shaft, which lies at about a 90 degree shaft angle with respect to the drive shaft.
Outboard motors also commonly employ a forward/neutral/reverse-type transmission which operates between the drive shaft and the propulsion shaft. The transmission typically includes a drive pinion and a pair of oppositely rotating driven bevel gears that are journaled within a lower unit of the outboard motor. A dog clutch sleeve couples the propulsion shaft to one of the driven bevel gears to rotate the propeller in either rotational direction to establish a forward or reverse drive condition.
An actuator actuates the clutch. In a conventional transmission, the actuator moves the dog clutch sleeve into engagement with the front gear to establish a forward drive condition, and moves the dog clutch sleeve into engagement with the rear gear to establish a reverse drive condition. The conventional actuator involves a plunger actuated by a cam. A spring, acting on an opposite end of the plunger from the cam, forces the plunger to follow the cam. The spring thus forces the dog clutch sleeve to engage the front gear. To disengage the clutch and to engage the clutch with the rear gear, the cam forces the plunger and the clutch out of engagement and moves the clutch into engagement with the rear gear.
Several drawbacks are associated with the conventional type of transmission described above. The teeth of the gears and clutch are not static, and the synchronization of the teeth is not a constant condition. Under most conditions, the teeth of the clutch and the gears are out of phase. Thus, engagement may not be instantaneous and may not be as quick as the watercraft operator would like.
In addition, the instantaneous positive engagement between the clutch and the gear places a large load on the engine, especially when quickly shifting between forward and reverse drive conditions as performed when maneuvering within the tight confines of a marina or when quickly decelerating. Under such conditions, the engine is instantaneously engaged with the propulsion shaft and the impeller, which are rotating in an opposite direction from the direction in which the engine is attempting to drive them. Under such conditions, the engine may stall.